1. Field of the Invention
This invention relates generally to the field of manufacturing coated fibers. More specifically, the invention relates to methods and apparatus for coating of fibers used in oral hygiene.
2. Description of Related Art
Tooth decay and dental disease can be caused by bacterial action resulting from the formation of plaque about the teeth and/or the entrapment of food particles in interstices between the teeth. Removal of plaque and entrapped food particles reduces the incidence of caries, gingivitis, and mouth odors as well as generally improving oral hygiene. Conventional brushing has been found to be inadequate for removing all entrapped food particles and plaque. To supplement brushing, dental flosses and tapes have been recommended.
Dental flosses with a formulation of a waxed coating applied to the dental thread have been found to be easier to insert between adjacent teeth than unwaxed floss due to the reduced friction of the waxed fiber against tooth enamel. Additives to color or flavor the floss, or to enhance the floss's ability to fight tooth decay can be added to the wax formulation before application to the floss, with the wax acting as a carrier for the additives.
Conventionally, wax has been applied to the floss by direct contact with hot, molten wax, either by dragging the floss through a molten bath of wax or across a rotating surface covered in molten wax. In the latter designated "roller method," molten wax is delivered to the rotating cylinder by submerging a lower portion of the roller in a molten bath of wax containing the coating formulation. The coating is transferred to the floss as it moves in contact across the top of the roller. The roller method of manufacturing coated fibers has certain disadvantages.
A primary disadvantage is that the roller method exposes the coating formulation to the atmosphere for prolonged periods of time resulting in increased oxidation of the formulation. The oxidation of the formulation before application decreases its subsequent chemical stability resulting in a diminished shelf-life of the final dental product. Also, oxidation of the formulation results in an undesirable appearance to the coating leading to consumer avoidance of the product. To avoid these difficulties, the formulation is frequently discarded and replaced during the manufacturing process. However, frequent replenishment results in increased waste and manufacturing expense. The roller method also results in an inconsistent application level along the length of a the fiber resulting in uneven coating levels.
Additionally, to keep the roller formulation flowable, it must remain heated throughout the application process. Heating increases the rate of oxidation and drives up manufacturing costs through increased energy expenditure. Heating also prevents ease of handling the formulation with heated formulation frequently splashing on to manufacturing equipment thereby increasing capital depreciation and maintenance costs. Additionally, heating increases the rate of evaporation of volatile additives, such as flavor oils, that are added to the coating formulation. Loss of these additives also increases manufacturing costs and leads to unwanted deviations from the chemical composition of the coating formulation. Heating and exposure of the formulation also pollute the manufacturing plant, requiring extraction of the volatilized fumes to prevent worker exposure to their potentially noxious effects.
Finally, the roller method is a `wet` process that is detrimental to a characteristic of the dental product--i.e., fiber bulking that is desirable. The application of `wet` coatings with the subsequent required drying process required (due to the heavy weight of the `wet` formulation) decreases to desired bulking property characteristics.
The present invention provides the advantage of a manufacturing method and apparatus; (1) that minimizes the oxidation and volatilization of fiber coating formulation and ingredients, (2) that decreases energy and manufacturing costs, (3) that increases safety for plant workers and (4) that preserves desired characteristics of the oral hygiene product fiber.